The present invention relates to a device for controlling the operation of a clutch. More particularly, the present invention relates to a device for controlling a clutch transmitting torque to a power takeoff (PTO) of a farm vehicle, to which the following description refers purely by way of example.
Farm vehicles normally comprise a power takeoff activated and deactivated by a clutch, which is engaged and released by a control device. One known control device comprises a two-position hand-operated lever, and a mechanical transmission for engaging and releasing the clutch directly. Mechanical control devices of the above type enable the torque transmission to be modulated by the operator for gradual or fast engagement as required.
The transmission of increasingly higher torques through the power takeoff calls for increasingly larger clutches requiring more and more force to operate, whereby mechanical control devices in some instances become inadequate. This has led to the development of hydraulic control devices for engaging and releasing the clutch by means of a hydraulic cylinder, which is supplied with hydraulic fluid under pressure by a pump and controlled selectively by a valve in turn controlled by a normally mechanical control member.
While enabling fairly high power transmission, control devices of the above type involve several drawbacks however by comprising open/closed valves for engaging the clutch with a predetermined torque transmission ramp which cannot be modified by the control member, thus preventing engagement of the clutch from being modulated by the mechanical control member.